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Title: First report of leaf spot on horseweed (Conyza canadensis L.) caused by Septoria erigerontis in Turkey

Author
item ERPER, ISMAIL - Ondokuz Mayis University
item TUNALI, BERNA - Ondokuz Mayis University
item Berner, Dana

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/22/2010
Publication Date: 7/1/2010
Citation: Erper, I., Tunali, B., Berner, D.K. 2010. First report of leaf spot on horseweed (Conyza canadensis L.) caused by Septoria erigerontis in Turkey. Plant Disease. 94:918.

Interpretive Summary: Horseweed is an invasive exotic weed in Turkey and a problematic native weed in the USA where herbicide-resistant populations of the weed have developed. These characteristics make horseweed a target for biological control efforts. During September 2009, leaf spots were observed on leaves of horseweed in Taflan, Turkey. A fungus designated 09-Y-TR1 was isolated from the diseased leaves. Fungus morphology was consistent with Septoria erigerontis. Comparison of DNA sequences with available sequences of Septoria erigerontis specimens showed a 99 percent match. DNA sequences for the fungus were deposited in GenBank. Stems and leaves of horseweed seedlings that were spray-inoculated with spores of the fungus exhibited disease symptoms consistent with those observed in the field. To our knowledge this is the first report of leaf spot on horseweed caused by S. erigerontis in Turkey where the fungus may have potential as a classical biological control agent. In the United States, S. erigerontis has been reported on horseweed in several states, and these isolates may have potential as biological control agents of horseweed, particularly herbicide-resistant horseweed, in the USA.

Technical Abstract: Horseweed (Conyza canadensis (L).Cronq.) is an invasive exotic weed in Turkey and a problematic native weed in the USA where glyphosate-resistant populations of the weed have developed. These characteristics make horseweed a target for biological control efforts. During September 2009, brown small leaf spots were observed on leaves of C. canadensis in Taflan, Turkey. Diseased tissue was surface disinfested and placed on moist filter paper in petri plates. A fungus designated 09-Y-TR1 was isolated from the diseased leaves. Cultures on PDA formed dark green to black colored colonies. Fungus morphology was consistent with Septoria erigerontis Peck. Comparison of the ITS 1 and 2 sequence with available sequences of vouchered Septoria erigerontis specimens (GenBank EF535638.1, AY489273.1; KACC 42355, CBS 109094) showed 447 of 450 and 446 of 450 identities, respectively. Nucleotide sequences for the ribosomal ITS regions (ITS 1 and 2, including 5.8S rDNA) were deposited in GenBank, accession no. GU952666. Stems and leaves of seven one-month-old seedlings were spray-inoculated with 10 ml of an aqueous suspension, containing 5 x 106 conidia/ml, per plant. Disease severity was evaluated 2 weeks after inoculation with a rating system based on a scale from 0 to 6, in which 0= no symptoms and 6 = leaf dead. The average disease rating on inoculated plants was 3.55. S. erigerontis was re-isolated from all inoculated plants. To our knowledge this is the first report of leaf spot on horseweed caused by S. erigerontis in Turkey where the fungus may have potential as a classical biological control agent. In the USA, S. erigerontis has been reported on horseweed in several states, and these isolates may have potential as biological control agents of horseweed, particularly glyphosate-resistant horseweed, in the USA.